The uneven distribution of fuel to the different fuel cells upon startup can lead to individual fuel cell fuel starvation, voltage reversal, and carbon corrosion, which ultimately results in severe performance loss.
In U.S. patent application Ser. No. 10/269,654, filed Oct. 10, 2002, now U.S. Pat. No. 6,924,056, a fuel cell, fuel inlet flow control apparatus divides the fuel flow several times, successively, in a cascade fashion to provide a number of separate flows, and then spreads the flow so as to distribute the fuel substantially uniformly across the entrances to all of the fuel flow fields in the fuel cell stack. Fuel flow transients approach the fuel flow fields of all of the fuel cells in the stack substantially simultaneously and at substantially the same flow rate, during startup and other transient fuel flow conditions. In a disclosed embodiment, the flow is split successively four times and then the flow through all of the outlet passages from the cascade region impinges on a flat surface, which spreads the flow uniformly. Although the cascade fuel distributor does distribute the fuel quite evenly, it has a significant pressure loss, and the volume consumed thereby is too large for certain applications. Geometrical constraints may prevent optimal design, in certain applications.